Flames of Darkness
by Masterofbalance
Summary: When a shadow from the past creeps up on them, Rin and the gang will have to turn to an ally no one knew existed. Rated M for gore in later chapters.
1. Chapter 1

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**Disclaimer: I do not and possibly will never in anyway own the characters of Blue Exorcist.**

Flames of Darkness

(In Gehenna)

Deep inside the darkest abyss one can hear the screams of terror as all that could be seen was flames that burned of sapphire, piercing through the endless shadows as it slowly grew silent. After a while out walk a half-naked male that seemed about 19 years of age, he had well-toned muscles, eyes of the same color as his flame with red irises, jet-black hair, and a black fur tipped tail that was swaying left to right.

Suddenly the man's eyes glowed as he was covered in the darkness of the abyss and let out a bloodthirsty screech that was heard by everyone in Gehenna; everybody reacted with looks of fear and dread like the end is near all but a certain demon lord that was sitting on his throne trying to find noticeably powerful people to be used as vessels for the elite class demons.

After hearing the screech said demon lord's thoughts were "Crap, the locking him up for years thing is something he will understand so I will be forgiven for that BUT, he would have wanted an update of important things." "Oh I can already feel the pain that he is going to inflict on me after explaining things to him." he sighed.

(Time skip three weeks in Assiah)

In True Cross Academy there was a certain man who seemed lost in thought. He was thinking about what his brother told him the day before.

(Flashback)

The man was sitting in his desk reading a shoujo manga about a young boy falling in love with his even younger sister. As a trickle of blood was running down his nose another male with green hair came in the said boy then said "Nii-san, what are you doing."

The other man just froze up and cleaned his nose and said "Amaimon, what are you doing here this time still trying to get our younger brother to play with you?"

The one now revealed as Amaimon just frowned as he said "Don't remind me he refuses to play; anyway I came because father has a message for you." The other man raised an eyebrow in curiosity "Really that's rare, what might he want to tell me." Amaimon just replied by saying "He's awake."

(Flashback end)

He was rubbing his temples as he thought about what 'He' would do if he came to Assiah, then a knock on the door "You may enter" he said then the door opened to reveal a navy blue haired boy that seemed to be about 15, he had a black tail and a sword on his back. "Ahhhh, Rin how are you today." he said with his usually borderline pedophilic smile of his.

Rin just answered "Don't try to be all cheerful Mephisto, what do you want?" Mephisto just chuckled before saying "Straight to the point as always, okay the reason I called you here was because your brother saying you have a stalker." Rin just narrowed his eyes and said "If you can call the demon king of earth a stalker."

Mephisto just nodded confirming the seriousness of the conversation then said "Since he never done anything to harsh recently just ignore him or comply, I'll let you decide you may leave" he said before he started to think about 'Him' again. "Oi, you there" said Rin as he was watching Mephisto with a raised eyebrow.

Mephisto was so startled by the sudden noise he fell from his seat, when he recovered he said "What, I told you to leave." Rin frowned and said "No, you said may leave and I'm not leaving until I say something first." Then Mephisto became intrigued "And may I ask what exactly may that be." As Rin started to talk the door then was slammed open then revealed a cloaked figure with sapphire blue eyes.

Mephisto was scared shitless at his sudden appearance "Ahhhh", don't hurt me." The cloaked figure just looked at him before saying "Why would I hurt you? You didn't do anything to piss me off at the moment...Wait, DID YOU?"

Mephisto was panicking at the figure's growing anger, he was about to say something before he was interrupted by Rin, "Who the hell are you?" he shouted. The cloaked figure just stared at him with his sapphire eyes that felt like it was piercing his soul, before saying "Are you Rin Okumura, son of Satan?" Rin just took a step back ready for anything while Mephisto was shaking in a corner too afraid of getting between the figure and Rin.

As the figure saw Rin enter a stance for combat he just narrowed his eyes, then just as suddenly a wave of killing intent washed over the entire room. Even Mephisto who was behind the figure got sick to the stomach for being surround by the aura, but Rin who took the full force of the blast found himself on his knees unable to move under the pressure. The figure then looked at Mephisto who jumped up ready to run away, even though he knew it was futile, as words left the figures mouth.

"Why doesn't he know about me?" Mephisto then replied with "W-w-well, I wasn't supposed to tell him anything about you, as you weren't supposed to know about him." He was then silenced by the figures sapphire eyes glowing as the room started to become darker, "What!" the figure said in a threatening tone.

Rin who had enough had drawn kurikara and tried to slash him, but was amazed when his arm was stopped by a slender, black tail. The man then turned his head and looked at Rin before saying "Poor thing, you don't know anything do you?" Rin who was brimming with anger had just said "Let me go!" as the tail let go of his arm he jumped back and shouted "I'm going to ask you one more time, WHO ARE YOU?"

The man replied by taking off his hood revealing black hair, pointed ears, and long pointed canines that resembled fangs, he then said "I'm Kurai, Satan's first son and your eldest brother."


	2. Chapter 2

**Disclaimer: I do not in any way, shape or form own Blue Exorcist nor will I ever.**

Flames of Darkness 2

(In Assiah)

Rin Okumura was processing what he just heard "W-w-what did you say?" he asked. Kurai just sighed "Like I said, I'm your eldest brother and have come to meet you." Mephisto who was still close to them tried to escape, until he was grabbed by Kurai that is. "HAVE MERCY ON ME!" he yelled trying to get free. "Mephisto, before you crap your pants, I am not going to do anything yet like I said I'm just meeting Rin today." Kurai said. Rin let his jaw drop to the floor "Why is Mephisto so afraid of you?" he asked. Kurai looked as if he was thinking then began to talk, "Because when we were younger I traumatized him by testing how sadistic I really was, too bad but it seemed to carry on over the years." Mephisto then started to talk "Testing, what you did was not testing: you threw off a cliff, destroyed my tail so much it won't be suitable for public eyes, punished me for insulting about Amaimon, and burned me with your flames. Testing is a 'HUGE' understatement." Rin sweat-dropped at this before thinking, "Just how powerful is he?" Kurai looked over to him before saying "So you want to know how powerful I am?" Rin jumped out of his skin with this "D-d-did you just read my mind?" he asked. Kurai frowned "Well I can like you probably can if you concentrate enough that is, but no it's because it written all over your face." Mephisto just thought "Man, Nii-san is scary." He was brought out of his thinking process by Kurai yelling "I HEARD THAT MEPHISTO!" Then he was gone and if you listen really closely you could hear someone screaming like a little girl of in the distance. After Kurai muttered something about gagging and torturing a pedophile like person before turning his attention onto Rin "Now what were we talking about before we were interrupted?" Rin was confused by how can someone that can make Mephisto do that be so forgetful before he looked at the clock "Shit, I'm late for class." He was about to start running when he was grabbed by Kurai who whistled a tune. Next thing Rin knew he was outside the classroom when he turned toward his older brother, "When you get as old as I am you have nothing to do but learn things, including things like that, anyway since Mephisto fled he can't excuse you even though he probably wouldn't anyway so we'll talk later." Kurai said before whistling the tune again and disappearing. Rin opened the door then was greeted by a "Your late Okumura!" Then Rin noticed why Kurai left, he didn't want to explain why not to put another tardy on Rin's report or so he thought he actually thought his job was done. Since he couldn't defend he just took his seat next to Shiemi who seemed worried for him. "Rin, you seem angry is there something wrong?" she whispered. Rin who didn't want to worry her just said "It's okay Shiemi just thinking about something" She was glad to found out he was alright but became curious on what he was thinking about, after all how is she supposed to know he was thinking about Kurai and what his next move will be.

(Time skip after class)

As soon as class ended Rin was showered by questions as everyone knew he was called into Mephisto's office they didn't know why though. "Oi Okumura, why where you called to the headmaster's office?" asked Ryuji. "Come on Bon, he doesn't need to answer if he doesn't want to if he doesn't want to." stated Shima. "Quiet Shima, you know full well you want to know to." said Bon. Rin now getting irritant of listening to them bicker just said "He just wanted to talk about Amaimon okay, now SHUT UP!"

As if on cue, said demon king called "Otouto, come on let's play a game." Everyone got shocked because if you can hear him, he must be close however this situation got Rin thinking "Hmmm, if Kurai could do that to Mephisto. Then. What. About." He was cut out of his thoughts when he heard "AHHH ONII-SAMA, I DID NOTHING WRONG PLEASE FORGIVE ME!"

Without realizing it Rin said out loud "Oh, so that's what happens to him... OH SHIT." Everyone was just staring at him, waiting for an explanation of what just happened. He was stuttering "W-w-well y-you see I kind of found out his greatest fear." after all he was telling the truth, every demon that has ever met him knows better than to piss of Kurai.

This ended when someone came through the door "Oi Rin, I finally remembered what we were talking about." Before anyone could see Rin ran to the door and snatched up Kurai then they vanished. "What the heck happened?" shouted Ryuji. Izumo said "I don't know, but I sensed an extremely powerful presence a little while ago."

(With Rin and Kurai)

"What was that about, you should have just asked if you wanted to hug me." said Kurai. Rin who was panting just glared at him, "You can't just move around freely in an exorcist academy... and WHERE IN THE HECK DID YOU GO?"

Kurai with a confused expression on just said "I told you I was going to take care of a pedophile like person sorry; I took so long I was actually having fun." Rin sweat-dropped again before saying "Listen, if you came to fight me just get it over with, I just want to go to sleep after this stressful day." Kurai raised an eyebrow before becoming completely serious and said "I didn't come here to fight, but if you want to I guess we can spar a little after all you are still wondering how powerful I am, aren't you?" Rin, not used to this side of him was taking a step back from his aura but something inside him was shaking, not from fear but from excitement "I know the perfect place to do it he said" Kurai grabbed him and whistled the tune once more before they disappeared.

(In the forest)

Rin and tired looking Kurai appeared in a clearing, Rin just looked confused at why he looked exhausted before they fought, He replied by saying "I don't do it too often because it takes a lot out of me, but worry not think of it as a sort of handicap or something. Rin's anger grew "Oh will I enjoy showing him how to talk to his superiors" he said while drawing Kurikara from its sheath. While Kurai took a deep breath and just stood there calmly "Come at me anytime." he said.

A completely agitated Rin just lunged himself at him swinging like a madman Kurai grabbed it with his hand and examined it "Oh this could actually hurt if it manages to cut me and the flames are a nice touch to." he then jumped back when flames were expelled from the sword. "Come on Rin if that's the best you can do this fight isn't going to be any fun." he said while dodging fireballs.

Elsewhere a beaten up Mephisto and Amaimon were watching as Kurai was 'fighting' their otouto. "Why can onii-sama get to play with Rin otouto?" asked Amaimon. "Because nii-san always gets the good stuff, I just hope he doesn't accidentally kill him." said Mephisto fearing for his otouto's life.

Back to the fighting Rin realized he wasn't making any progress with his attacks "Why. Can't. I. Hit. Him." he pondered then after his own fireball abstracted his own vision Kurai was gone, next thing he realized he felt a fist go into his stomach as he seen what he had for lunch.

"You are too cocky of your own power and take it for granted." He said before kicking him and sent him flying Kurai then appeared beside him "You use your flames recklessly and without true control" he hit him again, this time towards the ground "And finally you lost control of your emotions and charged blindly, that's how you get consumed by your own flames". He then took Kurikara and sheathed it. "That was pathetic you could only fight with the help of a demon sword and fathers power, if you fought any other demon king other than Amaimon they would've killed you by now." He then coated himself in his own sapphire flames "Perhaps I should break this." he said.

Rin who was hearing all this gathered as much flames as he could and threw a fireball the size of a large boulder at Kurai who simply deflected it with a wave of his hand. Then his calm expression came back "Sorry Rin, I was just so disappointed just now, I heard you beat Amaimon and I thought you were stronger so I didn't hold back as much as I normally would." He then proceed to look up "I'm leaving him up to you guys, make sure he gets stronger and you." he turned toward some trees and out came Shura, sword drawn ready to defend herself, but then she heard "Help them and keep him safe." With that he disappeared. Shura who was left there picked up the injured Rin and sighed "Four-eyes isn't going to like this when he comes back."

**This story will be going onto Hiatus until I write more chapters. Just so you know I only write when I feel inspired to do so but lately there isn't inspiration for me to attempt to even continue so expect it to be long.**

**Also I have a poll on my profile on what series to do when I get inspired again.**


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